JP6723545B2 - Positive electrode active material for secondary battery, method for producing the same, and secondary battery including the same - Google Patents

Description

This application claims the benefit of priority based on Korean Patent Application No. 2016-0026224 dated March 4, 2016 and Korean Patent Application No. 2017-0027879 dated March 3, 2017, and the relevant Korean patent All contents disclosed in the document of the application are incorporated as part of the present specification.

The present invention relates to a positive electrode active material for a secondary battery, which can improve charge/discharge characteristics of the battery, a method for producing the same, and a secondary battery including the same.

The demand for secondary batteries as an energy source is rapidly increasing with the technological development and the increase in demand for mobile devices. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.

However, the lithium secondary battery has a problem that its life is rapidly reduced as it is repeatedly charged and discharged. Especially at high temperatures, such problems are more serious. This is because the electrolyte is decomposed or the active material is deteriorated due to the moisture and other influences inside the battery, and the internal resistance of the battery is increased.

Therefore, the positive electrode active material for a lithium secondary battery, which is currently actively researched and developed, is LiCoO ₂ having a layered structure. LiCoO ₂ is excellent in life characteristics and charging/discharging efficiency and is most often used, but its structural stability is low and its application to a battery capacity increasing technology is limited.

As a positive electrode active material for use in place _{of, LiNiO 2, LiMnO 2, LiMn} 2 O 4, LiFePO 4, Li (Ni x Co y Mn z) various lithium composite metal oxides such as _{O 2} was developed .. Among them, LiNiO ₂ has an advantage that it exhibits a battery characteristic of high discharge capacity, but it has a problem that it is difficult to synthesize by a simple solid-phase reaction, and thermal stability and cycle characteristics are low. Further, a lithium manganese-based oxide such as LiMnO ₂ or LiMn ₂ O ₄ has the advantages of excellent thermal stability and low cost, but has the problems of small capacity and low high-temperature characteristics. In particular, in the case of LiMn ₂ O ₄ , although it is partially commercialized as an inexpensive product, the life characteristics are not good due to structural deformation (Jahn-Teller distortion) due to Mn ³⁺ . In addition, since LiFePO ₄ is inexpensive and excellent in safety, various studies are currently being carried out for hybrid electric vehicles (HEVs), but due to its low conductivity, it cannot be applied to other fields. difficult.

Such circumstances, substances bathed most spotlight recently as an alternative cathode active material LiCoO ₂ is of lithium nickel manganese cobalt _{oxide, Li (Ni x Co y Mn} z) O 2 ( In this case, the x, y, z Are the atomic fractions of the respective oxide composition elements, which are 0<x≦1, 0<y≦1, 0<z≦1, and 0<x+y+z≦1. This material is cheaper than LiCoO ₂ and has the advantage that it can be used for high capacity and high voltage, but has the disadvantage of poor rate capability and high temperature life characteristics.

Therefore, there is an urgent need for a method for producing a positive electrode active material that can improve the performance of a lithium secondary battery by changing the composition of the lithium mixed metal oxide or controlling the crystal structure.

A first problem to be solved by the present invention is to provide a positive electrode active material for a secondary battery and a method for producing the same, which can solve the above problems and improve the charge/discharge characteristics of the battery. is there.

A second problem to be solved by the present invention is to provide a positive electrode containing the positive electrode active material, a lithium secondary battery, a battery module and a battery pack.

According to an embodiment of the present invention to solve the above problems, a core, a shell surrounding the core, and a three-dimensional mesh located between the core and the shell and connecting the core and the shell. The core, the shell, and the three-dimensional network structure in the buffer layer each independently include a lithium composite metal oxide and have a BET specific surface area of 0.2 m ² / g~0.5m a ² / g, porosity is 30 vol%, the positive electrode active material for a secondary battery an average particle size _{(D 50)} is 8μm~15μm is provided.

In addition, according to another embodiment of the present invention, the nickel source material, the cobalt source material and the M1 source material (wherein M1 is at least one element selected from the group consisting of Al and Mn). An ammonium cation-containing complex forming agent and a basic compound are added to a mixture of metal source materials, and a coprecipitation reaction is performed at pH 11 to pH 13 to prepare a reaction solution in which a seed of a metal-containing hydroxide or oxyhydroxide is formed. In the preparing step, an ammonium cation-containing complex forming agent and a basic compound are added to the reaction solution until the pH of the reaction solution becomes 8 or more and less than 11, and the metal-containing hydroxide or oxyhydroxide particles are added. And a step of growing the metal-containing hydroxide or oxyhydroxide particles thus grown, wherein the lithium source material and the M3 source material (wherein M3 is selected from the group consisting of W, Mo and Cr). One or two or more elements) and then heat-treating the mixture are provided.

According to still another embodiment of the present invention, there is provided a positive electrode for a secondary battery, a lithium secondary battery, a battery module, and a battery pack that include the above-described positive electrode active material.

In addition, specific details of the embodiments of the present invention are incorporated in the following detailed description.

The secondary battery positive electrode active material according to the present invention further comprises a network-structured lithium composite metal oxide buffer layer connected between the core and the shell in the particles having the core-shell structure. By having a specific structure formed and controlling both the specific surface area and the average particle size of the active material particles and the porosity, the destruction of the active material due to the rolling process during the production of the electrode is minimized, and the electrolyte solution The reactivity with the compound is maximized, and the particles forming the shell have a crystal structure with an orientation that facilitates insertion and desorption of lithium ions, so that the output characteristics and life characteristics of the secondary battery can be improved. .. As a result, the positive electrode active material according to the present invention is a battery that requires high capacity, long life and thermal stability, such as a battery for an automobile or a battery for an electric tool, and particularly, a performance deterioration at a high voltage such as a battery for an automobile. It is useful as a positive electrode active material in batteries that require minimization of

The following drawings attached to the present specification illustrate preferred embodiments of the present invention and serve to more easily understand the technical idea of the present invention together with the contents of the above-mentioned invention. The present invention should not be construed as being limited to the matters described in the drawings.

1 is a cross-sectional structural view schematically showing a positive electrode active material for a secondary battery according to an embodiment of the present invention. 1 is a photograph of the positive electrode active material manufactured in Example 1 observed with a field emission scanning electron microscope (FE-SEM) (observation magnification=30000 times).

Hereinafter, the present invention will be described in more detail in order to facilitate understanding of the present invention.

The terms and words used in the specification and the claims should not be construed as limited to their ordinary or dictionary meanings, and the inventors shall describe their invention in the best way possible. Therefore, according to the principle that the concept of terms can be defined as appropriate, the meaning and concept should be interpreted in accordance with the technical idea of the present invention.

A positive electrode active material for a secondary battery according to an embodiment of the present invention,
With the core,
A shell located around the core,
A buffer layer that is located between the core and the shell and that connects the core and the shell and that includes a three-dimensional network structure and a void.
The three-dimensional network structure in the core, the shell and the buffer layer each independently contains a lithium mixed metal oxide,
BET specific surface area of 0.2m ² /g~0.5m ² / g, porosity is 30 vol%, an average particle size _{(D 50)} is 8Myuemu～15myuemu.

Thus, the positive electrode active material for a secondary battery according to an embodiment of the present invention is a particle having a core-shell structure having a three-dimensional network structure in which the core and the shell are connected between the core and the shell. By having a structure in which the buffer layer is further formed, at the time of manufacturing the electrode, the destruction of the active material by the rolling process is minimized, the reactivity with the electrolytic solution is maximized, and the particles forming the shell are made of lithium ions. It has an oriented crystal structure that is easy to insert and remove, which can improve the output characteristics and life characteristics of the secondary battery. In addition, since the specific surface area of the particles, the average particle diameter, and the porosity of the positive electrode active material are both controlled, the charge/discharge characteristics can be further improved when the battery is applied.

FIG. 1 is a cross-sectional structural view schematically showing a positive electrode active material for a secondary battery according to an embodiment of the present invention. FIG. 1 is an example for explaining the present invention, and the present invention is not limited to this.

Referring to FIG. 1, a positive electrode active material 10 for a secondary battery according to an exemplary embodiment of the present invention includes a core 1, a shell 2 surrounding the core, and the core surrounded by the core and the shell. And a buffer layer 3 located at 1. The buffer layer 3 includes a void 3a and a three-dimensional mesh structure 3b.

Specifically, in the positive electrode active material 10, the core 1 is a lithium composite metal oxide (lithium intercalation compound) as a compound capable of reversible intercalation and deintercalation of lithium (lithium intercalation compound). Hereinafter, it is simply referred to as “first lithium mixed metal oxide”).

The core 1 may be composed of single particles of the above-mentioned first lithium mixed metal oxide, or may be composed of secondary particles obtained by aggregating the primary particles of the first lithium mixed metal oxide. Good. At this time, the primary particles may or may not be uniform.

In addition, in the positive electrode active material 10, the shell 2 is a lithium composite metal oxide (hereinafter, simply referred to as a lithium intercalation compound) that is a compound capable of reversible intercalation and deintercalation of lithium. (Hereinafter referred to as “second lithium mixed metal oxide”).

The second lithium mixed metal oxide may be crystal-oriented particles that are radially grown from the center of the positive electrode active material to the outside. In this way, the particles of the second lithium mixed metal oxide forming the shell have the crystal orientation of the same composition by having the crystal orientation in the direction in which lithium insertion and desorption are smooth. Higher output characteristics can be achieved compared to non-particles.

Specifically, in the shell 2, the particles of the second lithium mixed metal oxide may have various shapes such as a polygon such as a hexahedron, a cylinder, a fibrous shape, or a scaly shape. More specifically, the particles of the second lithium mixed metal oxide may be fibrous having an aspect ratio of 1.5 or more. When the aspect ratio of the particles of the second lithium mixed metal oxide forming the shell is less than 1.5, uniform particle growth may not be performed, and the electrochemical characteristics may deteriorate. At this time, the aspect ratio is such that, with respect to the length in the major axis direction that passes through the center of the second lithium mixed metal oxide particle, a short length that passes through the center of the oxide particle and is perpendicular to the major axis. It means the ratio of the length in the axial direction.

In addition, the shell 2 may further include voids formed between the particles of the second lithium mixed metal oxide.

On the other hand, the buffer layer 3 including the void 3a and the three-dimensional mesh structure 3b that connects the core and the shell is located between the core 1 and the shell 2 described above.

In the buffer layer 3, the voids 3a are formed in the process in which the active material particles are converted into a hollow structure as the pH of the reaction product is controlled during the production of the active material. A space is formed between the shell 2 and the shell 2 to cushion the rolling during manufacturing of the electrode. In addition, the electrolytic solution can easily penetrate into the positive electrode active material and react with the core to increase the reaction area of the active material with the electrolytic solution.

Thus, in addition to the voids 3a formed in the buffer layer, voids that may be formed between the lithium mixed metal oxide particles contained in the shell may be selectively included. The positive electrode active material may have a porosity of 30% by volume or less, more specifically 2 to 30% by volume, based on the total volume of the positive electrode active material. By having the porosity within the above range, it is possible to exhibit an excellent buffering effect and an effect of increasing the reaction area with the electrolytic solution without lowering the mechanical strength of the active material. Further, considering the remarkable improvement effect due to the formation of the voids, the positive electrode active material may exhibit a porosity of 5 to 25% by volume with respect to the total volume of the positive electrode active material. At this time, the porosity of the positive electrode active material can be measured by cross-sectional analysis of particles using a focused ion beam (FIB) or mercury porosimetry.

Further, in the buffer layer 3, the three-dimensional network structure 3b is formed in the process in which the active material particles are converted into a hollow structure during the production of the active material to form an inner core. And serves to support the space between the core 1 and the shell 2. As a result, the three-dimensional network structure 3b, like the core 1 and the shell 2, is a lithium composite metal as a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound). An oxide (hereinafter simply referred to as “third lithium mixed metal oxide”) is included.

The positive electrode active material 10 according to an embodiment of the present invention having the above structure includes a lithium composite metal oxide, and a molar ratio of lithium and composite metal in the transition metal oxide (Li/Me molar ratio). ) May be 1 or more.

More specifically, the first to third lithium mixed metal oxides contained in the core, the shell and the buffer layer may each independently contain the compound of Chemical Formula 1 below.

(Chemical formula 1)
Li _a Ni _1-x-y Co _x M1 _y M3 _z M2 _w O ₂
(In the above Chemical Formula 1, M1 is at least one selected from the group consisting of Al and Mn, and M2 is any one selected from the group consisting of Zr, Ti, Mg, Ta and Nb. Or two or more elements, and M3 is one or more elements selected from the group consisting of W, Mo and Cr, and 1.0≦a≦1.5,0 <x≦0.5, 0<y≦0.5, 0.0005≦z≦0.03, 0≦w≦0.02, 0<x+y≦0.7)

The composition of the lithium mixed metal oxide represented by Chemical Formula 1 is an average composition of the entire active material.

The positive electrode active material according to an embodiment of the present invention includes the lithium mixed metal oxide having the composition of Chemical Formula 1 described above, and thus has excellent structural stability and can improve battery life characteristics. it can.

Specifically, in the lithium mixed metal oxide of Chemical Formula 1, Li may have a content corresponding to a, that is, 1.0≦a≦1.5. If a is less than 1.0, the capacity may decrease, and if it exceeds 1.5, the particles may sinter in the firing step, which may make it difficult to manufacture the active material. Considering the balance of the effect of improving the capacity characteristics of the positive electrode active material by controlling the Li content and the sinterability during the production of the active material, the Li is more specifically 1.0≦a≦1. It may be included in a content of 0.15.

In addition, in the lithium mixed metal oxide of Chemical Formula 1, Ni may be included in a content corresponding to 1-xy, that is, a content of 0.3≦1-xy<1. When 1-x-y is less than 0.3, the capacity characteristic may be deteriorated, and when 1 or more, the high temperature stability may be deteriorated. Considering the remarkable effect of the capacity characteristic improving effect by including Ni, the Ni may be more specifically included in a content of 0.5≦1-xy<0.9.

In addition, in the lithium mixed metal oxide of Chemical Formula 1, Co may be included in a content corresponding to x, that is, a content of 0<x≦0.5. When x is 0, the capacity and output characteristics may deteriorate, and when it exceeds 0.5, the cost may increase. Considering the conspicuousness of the effect of improving the capacitance characteristic by including Co, the Co may be more specifically included in the content of 0.10≦x≦0.35.

The M1 may be included in a content corresponding to y, that is, a content of 0<y≦0.5. When y is 0, the improvement effect due to inclusion of M1 cannot be obtained, and when y exceeds 0.5, the output characteristics and capacity characteristics of the battery may rather be deteriorated. Considering the remarkable effect of improving the battery characteristics by including the M1 element, the M1 may be more specifically included in the content of 0<y≦0.2.

In addition, in the lithium mixed metal oxide of Chemical Formula 1, M3 is an element corresponding to Group 6 (VIB group) of the periodic table, and plays a role of suppressing particle growth during the firing step during the production of the active material particles. do. In the crystal structure of the positive electrode active material, M3 may replace a part of Ni, Co or M1 and may be present at a position where these elements should exist, or react with lithium to form a lithium oxide. You may. Thereby, the size of the crystal grains can be controlled by adjusting the content of M3 and the timing of incorporation. Specifically, the M3 may be any one or two or more elements selected from the group consisting of W, Mo and Cr, and more specifically, at least one of W and Cr. It may be one element. Among them, when M3 is W, the output characteristics are excellent, and when Cr is M, the life stability is more excellent.

The M3 may be included in the lithium mixed metal oxide of Chemical Formula 1 in an amount corresponding to z, that is, 0.0005≦z≦0.03. When z is less than 0.0005, it is not easy to realize an active material satisfying the above characteristics, and as a result, there is a possibility that the effect of improving output and life characteristics is not so great. Further, if z exceeds 0.03, distortion or collapse of the crystal structure may be induced, and movement of lithium ions may be hindered to reduce the battery capacity. Considering the realization of the particle structure by controlling the content of the M3 element and the conspicuous effect of improving the battery characteristics due to the control, the content may be more specifically 0.001≦z≦0.01.

In addition, the lithium mixed metal oxide of Chemical Formula 1 or the elements of Ni, Co and M1 in the lithium mixed metal oxide may be mixed with other elements in order to improve the battery characteristics by controlling the distribution of the metal elements in the active material. It may be partially substituted or doped with the element, ie M2. The M2 may be any one or two or more elements selected from the group consisting of Zr, Ti, Mg, Ta and Nb, and more specifically, Ti or Mg. May be

The element of M2 may be included in an amount corresponding to w, that is, a content of 0≦w≦0.02 within a range that does not deteriorate the characteristics of the positive electrode active material.

Further, in the positive electrode active material, the metal element of at least one of nickel, M1 and cobalt contained in the lithium mixed metal oxide of the chemical formula 1 may be any one of the core, the shell and the entire active material particles. It is possible to show increasing or decreasing concentration gradients within one region. Specifically, nickel, cobalt, and M1 contained in the positive electrode active material have a positive (+) average concentration profile in the positive electrode active material from the center of the particle to the surface of the particle or in the core and the cell. Alternatively, the distribution may be negative (-).

In the present invention, the concentration gradient or concentration profile of the metal element means the depth from the particle surface to the central portion when the X axis indicates the depth from the particle surface to the central portion and the Y axis indicates the content of the metal element. It means a graph showing the content of the metal element depending on the size. As an example, that the average slope of the concentration profile is positive means that the section of the central portion of the particle is relatively more located in the metal element than the surface portion of the particle. It means that the metal element is relatively more located on the surface portion of the particle than in the central section. In the present invention, the concentration gradient and concentration profile of the metal in the active material include X-ray photoelectron spectroscopy (XPS), ESCA (Electron Spectroscopy for Chemical Analysis), and electron beam microanalyzer. Electron Probe Micro Analyzer (EPMA), Inductively Coupled Plasma-Atomic Emission Spectrometer, ICP-AES, or Time-of-Flight Secondary Ion Mass Spectroscopy (TiP). -SIMS) and the like. For example, when the profile of the metal element in the active material is confirmed using XPS, the metal element ratio (atomic ratio) is measured for each etching time while etching the active material in the direction from the particle surface to the center. However, the concentration profile of the metal element can be confirmed from this.

Specifically, the metal element of at least one of nickel, cobalt and M1 is a metal element in any one region of the core, the shell and the entire active material particles, and more specifically, the metal element over the entire active material particles. May have a concentration gradient that continuously changes, and the gradient of the concentration gradient of the metal element may exhibit one or more values. With such a continuous concentration gradient, there is no abrupt phase boundary region from the center to the surface, the crystal structure is stabilized, and the thermal stability is increased. Further, when the gradient of the metal concentration gradient is constant, the effect of improving the structural stability can be further improved. Further, by varying the concentration of each metal in the active material particles according to the concentration gradient, the characteristics of the metal can be easily utilized to further improve the battery performance improvement effect of the positive electrode active material.

In the present invention, “the metal concentration continuously exhibits a concentration gradient” means that the metal concentration exists in a concentration distribution that gradually changes over the entire particle. Specifically, the concentration distribution is such that the change in metal concentration per 1 μm in the particles is 0.1 to 30 atom %, more specifically, based on the total atomic weight of the metal contained in the positive electrode active material. May vary from 0.1 to 20 atom %, more specifically from 1 to 10 atom %.

More specifically, in the positive electrode active material according to an embodiment of the present invention, the metal element of at least one of nickel, cobalt, and M1 exhibits a concentration gradient that continuously changes throughout the active material particles. The gradient of the concentration gradient of the metal element in the active material particles may exhibit one or more values.

Further, in the positive electrode active material according to the embodiment of the present invention, the metal element of at least one of nickel, cobalt and M1 has a concentration gradient that continuously and independently changes in the core and the shell. The gradient of the concentration gradient of the metal element in the core and the shell may be the same or different from each other.

More specifically, in the positive electrode active material according to an embodiment of the present invention, the concentration of nickel contained in the positive electrode active material has a continuous concentration gradient from the center of the active material particle toward the surface of the particle. Or may independently decrease in the core and shell, respectively, with a continuous concentration gradient from the center of the active material particle to the surface of the particle. At this time, the gradient of the nickel concentration gradient may be constant from the center to the surface of the positive electrode active material particles, or within the core and the shell. In this way, when the concentration of nickel is maintained at a high concentration in the center of the particles in the active material particles and the concentration gradient decreases toward the particle surface side, thermal stability is exhibited and a decrease in capacity is prevented. can do.

In addition, in the positive electrode active material according to one embodiment of the present invention, the concentration of cobalt contained in the positive electrode active material increases with a continuous concentration gradient from the center of the active material particle toward the surface of the particle. Or; independently in the core and shell, each may increase with a continuous concentration gradient from the center of the active material particle to the surface of the particle. At this time, the gradient of the cobalt concentration gradient may be constant from the center to the surface of the positive electrode active material particles, or within the core and the shell. In this way, when the cobalt concentration in the active material particles maintains a low concentration at the center of the particles and includes a concentration gradient in which the concentration increases toward the surface side, the amount of cobalt used is reduced and the capacity is reduced. Can be prevented.

In the positive electrode active material according to the embodiment of the present invention, the concentration of M1 contained in the positive electrode active material increases with a continuous concentration gradient from the center of the active material particle toward the surface of the particle. Or independently within the core and shell, and may increase with a continuous concentration gradient from the center of the active material particle to the surface of the particle. At this time, the gradient of the concentration gradient of M1 may be constant from the center to the surface of the positive electrode active material particles, or within the core and the shell. As described above, when the concentration of M1 is kept low in the center of the active material particle and the concentration gradient increases toward the particle surface side, the thermal stability is improved without decreasing the capacity. can do. More specifically, the M1 may be manganese (Mn).

Further, in the positive electrode active material according to one embodiment of the present invention, the content of nickel contained in the core may be larger than the content of nickel contained in the shell, and specifically, the core is And containing nickel in a content of 60 atomic% or more and less than 100 atomic% with respect to the total atomic weight of the metallic elements contained in the core, and the shell is 30 to 60 with respect to the total atomic weight of the metallic elements contained in the shell. Nickel may be contained in a content of less than atomic %.

Further, in the positive electrode active material according to the embodiment of the present invention, the content of cobalt contained in the core may be smaller than the content of cobalt contained in the shell.

In the positive electrode active material according to the embodiment of the present invention, the content of M1 contained in the core may be smaller than the content of M1 contained in the shell.

In the positive electrode active material according to the embodiment of the present invention, nickel, cobalt, and M1 each independently show a continuously changing concentration gradient over the entire active material particles, and the nickel concentration is: The active material particles have a continuous concentration gradient in the direction from the surface to the surface, and the concentrations of cobalt and M1 are independent of each other and are continuous in the direction from the center to the surface of the active material particles. May be increased.

In the positive electrode active material according to the embodiment of the present invention, nickel, cobalt and M1 each independently show a continuously changing concentration gradient in the core and the shell, and the concentration of nickel is the core. From the center to the interface between the core and the buffer layer and from the interface between the buffer layer and the shell to the surface of the shell with a continuous concentration gradient, and the concentrations of cobalt and M1 are independent of each other. It may be increased with a continuous concentration gradient from the center of the core to the interface between the core and the buffer layer, and from the interface between the buffer layer and the shell to the surface of the shell.

Thus, the concentration of nickel decreases and the concentrations of cobalt and M1 increase toward the surface side of the positive electrode active material particles partially or entirely within the active material. It can maintain its properties and exhibit thermal stability.

Further, the positive electrode active material according to one embodiment of the present invention may include polycrystalline lithium composite metal oxide particles having an average size of crystal particles of 200 nm or less, specifically 60 nm to 200 nm.

The average size of the crystal particles in the positive electrode active material is optimized so as to exhibit high output characteristics by controlling the content of the M3 element contained in the lithium mixed metal oxide at the time of its production and the firing conditions. It was done. Specifically, the average size of the crystal particles constituting the polycrystalline lithium mixed metal oxide is 60 nm to 150 nm, and in consideration of the remarkable effect of improving the output characteristics by controlling the crystal size, the average size of the crystal particles is More specifically, it may be 80 nm to 120 nm.

In the present invention, the term “polycrystal” means a crystal body composed of two or more crystal grains. Further, in the present invention, the crystalline particles forming the polycrystal mean primary particles, and the polycrystal means the form of secondary particles in which the primary particles are aggregated.

In addition, in the present invention, the average size of the crystal particles can be quantitatively analyzed by using the X-ray diffraction analysis of the lithium composite metal oxide particles. For example, the average size of the crystal particles can be quantitatively analyzed by putting the polycrystalline lithium mixed metal oxide particles in a holder and analyzing a diffraction grating that appears when the particles are irradiated with X-rays.

In addition, the positive electrode active material according to the embodiment of the present invention may have a nickel (Ni) disorder degree (Ni disorder) in the crystal of the lithium mixed metal oxide of 0.2 to 3.0%. By having such a low degree of Ni disorder, excellent cycle efficiency and capacity characteristics can be exhibited. More specifically, it may be 0.5 to 2%, and more specifically 0.5 to 1.5%.

In the present invention, the Ni disorder degree can be determined from the amount of Ni ions disordered to Li sites during the synthesis of the positive electrode active material. Specifically, the Ni disorder degree is obtained from a sample pattern by performing an atomic structure analysis using the Rietveld method and analyzing the relative amount of Ni ²⁺ ions occupying the Li site. After analyzing the relative occupancy ratio of oxygen sites by oxygen from each diffraction degree, the amount of Ni ions disordered to Li sites during synthesis can be determined from this. At this time, the oxygen occupancy z is interpreted as a number variable, the occupancy of Li and Ni is a single variable x that can be changed between two sites, and the occupancy of the Li site by the M1 ion is The occupancy of Ni site by Co, Ni and Ni ions is represented by the above chemical formula 1 and is treated at a constant level. The first cycle efficiency can be improved by decreasing the nickel disorder degree (%Ni ⁺ ) x and increasing the relative oxygen concentration z.

The positive electrode active material having the above structure may have an average particle diameter (D ₅₀ ) of 8 to ₁₅ μm in consideration of the specific surface area and the positive electrode mixture density. If the average particle size of the positive electrode active material is less than 8 μm, the stability of the lithium mixed metal oxide particles may decrease and the dispersibility in the active material layer may decrease due to aggregation between the positive electrode active materials. In this case, the output characteristics may be deteriorated due to the decrease in the mechanical strength of the positive electrode active material and the decrease in the specific surface area. Further, considering the effect of improving the rate characteristic and the initial capacity characteristic due to the specific structure, the average particle diameter (D ₅₀ ) may be 9 to 12 μm.

In the present invention, the average particle size (D ₅₀ ) of the positive electrode active material may be defined as the particle size based on 50% of the particle size distribution. In the present invention, the average particle diameter (D ₅₀ ) of the positive electrode active material particles may be, for example, a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM). The measurement can be performed using the electron microscope observation used or a laser diffraction method. When measuring by a laser diffraction method, more specifically, after dispersing the particles of the positive electrode active material in a dispersion medium, the particles are introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000) and about 28 kHz. After irradiating the ultrasonic waves of with the output of 60 W, the average particle size (D ₅₀ ) on the basis of 50% of the particle size distribution in the measuring device can be calculated.

In the positive electrode active material, the ratio of the radius of the core to the radius of the positive electrode active material particles is more than 0 and less than 0.4, and the interface between the buffer layer and the shell from the center of the active material particles to the radius of the positive electrode active material particles. The ratio of lengths up to 0 may be greater than 0 and less than 0.7.

In the positive electrode active material, the shell region determined by the following mathematical formula 1 may be 0.2 to less than 1, preferably 0.4 to 0.6.

(Formula 1)
Shell region=(radius of positive electrode active material−radius of core−thickness of buffer layer)/radius of positive electrode active material

When the core, the buffer layer, and the shell are formed in the positive electrode active material in the above-described ratio, and when the concentration gradient of the metal element is formed in each region, the concentration of nickel, cobalt, and manganese in the active material particles is increased. By controlling the distribution more optimally, the destruction of the active material due to the rolling process during electrode manufacturing is minimized, the reactivity with the electrolyte is maximized, and the output characteristics and life characteristics of the secondary battery are further improved. be able to.

In the present invention, the particle size of the core part can be measured by cross-sectional analysis of the particles using a focused ion beam (fib).

Further, the positive active material according to an embodiment of the present invention, BET specific surface area may be 0.2m ² /g~0.5m ² / g.

If the BET specific surface area of the positive electrode active material exceeds 0.5 m ² /g, the dispersibility of the positive electrode active material in the active material layer may decrease due to aggregation between the positive electrode active materials, and the resistance in the electrode may increase. If the BET specific surface area is less than 0.2 m ² /g, the dispersibility of the positive electrode active material itself and the capacity may decrease. In the present invention, the specific surface area of the positive electrode active material is measured by the BET (Brunauer-Emmett-Teller) method, and specifically, using BELSORP-mino II manufactured by BEL Japan under liquid nitrogen temperature ( It can be calculated from the nitrogen gas adsorption amount at 77K).

Further, the positive electrode active material according to one embodiment of the present invention can exhibit excellent capacity and charge/discharge characteristics by simultaneously satisfying the conditions of the average particle diameter and the BET specific surface area described above. Specifically, the positive active material may have a BET specific surface area of the average particle diameter _{(D 50)} and 0.2m ² /g~0.5m ² / g of 8Myuemu～15myuemu, more specifically the average particle size _{(D 50)} of 8μm~10μm and 0.25m ² /g~0.35m ² / BET specific surface area of g, and more specifically, the average particle size of less than or 8 [mu] m 10 [mu] m _{(D 50} ) And a BET specific surface area of more than 0.25 m ² /g and 0.35 m ² /g or less. In the present invention, the specific surface area of the positive electrode active material is measured by the BET (Brunauer-Emmett-Teller) method, and specifically, using BELSORP-mino II manufactured by BEL Japan under liquid nitrogen temperature ( It can be calculated from the nitrogen gas adsorption amount at 77K).

In addition, the positive electrode active material according to one embodiment of the present invention has boron (B), aluminum (Al), titanium (Ti), silicon (Si), tin (Sn), magnesium (on the surface of the active material particles). 1) a surface treatment layer containing at least one coating element capable of protecting the surface of the active material, such as Mg), iron (Fe), bismuth (Bi), antimony (Sb) or zirconium (Zr). It may further include more than one layer.

Specifically, the surface treatment layer may have a single-layer structure containing the coating elements described above, or may include two or more coating elements described above in the single layer. Further, the surface treatment layer may have a multilayer structure of two or more layers in which one or more surface treatment layers each containing the above coating element are repeatedly formed.

More specifically, when boron is used as the coating element, the surface treatment layer can be formed in the form of boron lithium oxide. In particular, since the boron lithium oxide can be uniformly formed on the surface of the positive electrode active material, it can exhibit a more excellent effect of protecting the positive electrode active material. The boron lithium oxide may be, for example, LiBO ₂ or Li ₂ B ₄ O ₇ , and may include one or a mixture of two or more thereof.

Further, the surface treatment layer may contain boron in an amount of 100 ppm to 2000 ppm, more specifically, 250 ppm to 1100 ppm.

Further, the boron lithium oxide contained in the surface treatment layer is 0.01 wt% to 1 wt%, specifically 0.05 wt% to 0.5 wt% with respect to the total weight of the positive electrode active material. May be included in quantity. When the content of the lithium boron oxide is less than 0.01% by weight, the surface treatment layer formed on the surface of the lithium mixed metal oxide becomes thin, which has the effect of suppressing a side reaction between the electrolytic solutions during charging and discharging. If the amount is more than 1% by weight, the surface treatment layer may become thick due to the excessive content of the lithium lithium oxide, which may result in a decrease in the electrochemical characteristics of the lithium secondary battery due to the increased resistance. there were.

In addition, according to an embodiment of the present invention, the surface treatment layer may be formed by dry-mixing a positive electrode active material containing a lithium mixed metal oxide with a boron-containing compound and then heat treating the mixture. Thereby, a part of the boron element contained in the surface treatment layer may be doped in the lithium mixed metal oxide of the positive electrode active material, and the boron doped in the lithium mixed metal oxide. The content of may have a concentration gradient that decreases from the surface to the inside of the lithium mixed metal oxide. In this way, when a concentration gradient of boron is formed from the surface treatment layer to the inside of the positive electrode active material, structural stability is increased and cycle characteristics can be improved.

When using aluminum as the coating element, the surface treatment layer may be formed in the form of aluminum oxide, and unlike boron, in the case of aluminum, a discontinuous pattern on the surface of the positive electrode active material, for example, The surface treatment layer may be formed in an island shape. Aluminum existing on the surface of the positive electrode active material reacts with hydrogen fluoride (HF) and is transformed into AlF ₃ , thereby protecting the surface of the active material from the attack of hydrogen fluoride. The aluminum may be specifically included in an oxide form such as Al ₂ O ₃ .

For example, the aluminum-containing surface treatment layer may be formed by dry-mixing a positive electrode active material containing a lithium mixed metal oxide with an aluminum-containing compound, and then heat treating the mixture. At this time, by controlling the particle size of the aluminum-containing compound, it is possible to suppress the crystal structure change of the aluminum oxide contained in the surface treatment layer, and as a result, it is possible to improve the cycle stability during charge and discharge.

In the case of the coating element such as titanium (Ti), silicon (Si), tin (Sn), magnesium (Mg), iron (Fe), bismuth (Bi), antimony (Sb) or zirconium (Zr), TiO 2 is used. _A surface treatment layer is formed on the surface of the positive electrode active material in the form of an oxide such as ₂ , SiO ₂ , SnO ₂ , MgO, Fe ₂ O ₃ , Bi ₂ O ₃ , Sb ₂ O ₃ , or ZrO _2. And serves to protect the positive electrode active material.

Also in the case of these coating elements, the surface treatment layer can be formed by the same method as for the aluminum.

On the other hand, the thickness of the surface treatment layer may be 10 nm to 1000 nm.

When the thickness of the surface treatment layer formed on the surface of the active material is 1000 nm or less, the internal resistance of the active material can be reduced, the discharge potential is prevented from lowering, and the current density (C-rate) changes. High discharge potential characteristics can be maintained. As a result, when the battery is applied, more excellent life characteristics and discharge voltage drop can be exhibited.

In addition, the positive electrode active material according to the embodiment of the present invention may have a tap density of 1.7 g/cc or more, or 1.7 g/cc to 2.5 g/cc. By having a high tap density in the above range, high capacity characteristics can be exhibited. In the present invention, the tap density of the positive electrode active material can be measured by using a normal tap density measuring device, and specifically, it can be measured by using a tap density tester.

Meanwhile, according to another embodiment of the present invention, a positive electrode active material according to an embodiment of the present invention having the above-described structure and physical properties includes a nickel source material, a cobalt source material, and an M1 source material (in this case, , M1 is at least one element selected from the group consisting of Al and Mn), the ammonium cation-containing complex-forming agent and the basic compound are added to a mixture of the metal source materials, and the mixture is added at pH 11 to pH 13. A step of preparing a reaction solution in which a seed of metal-containing hydroxide or oxyhydroxide is produced by coprecipitation reaction (step 1); and an ammonium cation-containing complex-forming agent and a basic compound are added to the reaction solution. Adding the reaction solution until the pH is 8 or more and less than 11 to grow particles of the metal-containing hydroxide or oxyhydroxide (Step 2); and the growing metal-containing hydroxide or oxyhydroxide. The particles of the product are mixed with a lithium source material and an M3 source material (where M3 is one or more elements selected from the group consisting of W, Mo and Cr), and then heat treated. It can be manufactured by a manufacturing method including a step (step 3). At this time, when the positive electrode active material further includes M2 (wherein M2 is any one or two or more elements selected from the group consisting of Zr, Ti, Mg, Ta and Nb), The M2 source material may be added when the mixture of the metal source materials in step 1 is manufactured, or the M2 source material may be added when mixed with the lithium source material in step 3. Accordingly, according to another embodiment of the present invention, there is provided a method for manufacturing the above positive electrode active material.

Hereinafter, each step will be described in more detail. In the manufacturing method for manufacturing the positive electrode active material, the step 1 is to add a mixture of metal source materials including nickel, cobalt, M1 and optionally M2 to an ammonium cation. It is a step of preparing a reaction solution in which a metal-containing hydroxide or oxyhydroxide seed is produced by adding a complexing agent-containing agent and a basic compound and performing coprecipitation reaction at pH 11 to pH 13.

Specifically, when preparing the mixture of the metal raw material, the nickel raw material, the cobalt raw material, the M1 containing raw material, and optionally the M2 containing raw material are mixed with a solvent, specifically water, or water. It may be produced by adding it to a mixture of a miscible organic solvent (specifically, alcohol, etc.) and water, or a solution containing each raw material, specifically, an aqueous solution, which is then prepared. You may mix and use it. At this time, each raw material may be used in an appropriate content in consideration of the content of each metal element in the finally produced lithium mixed metal oxide.

Specifically, the total number of moles of nickel ions, cobalt ions and manganese ions may be 0.5M to 2.5M, and more specifically 1M to 2.2M. Further, it is preferable to continuously supply the transition metal starting material in accordance with the deposition rate of the transition metal hydroxide so that the ion concentration is maintained.

As the raw material containing the above-mentioned metal element, acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide may be used, which is dissolved in water. As long as it exists, it is not particularly limited.

As an example, as the cobalt raw _{material, Co (OH) 2, CoOOH} , Co (OCOCH 3) 2 · 4H 2 O, Co (NO 3) 2 · 6H 2 O or _{Co (SO 4) 2 · 7H} 2 O And the like, and any one of these or a mixture of two or more may be used.

Further, as the nickel raw material, Ni(OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni(OH) ₂ .4H ₂ O, NiC ₂ O ₂ .2H ₂ O, Ni(NO ₃ ) ₂ .6H ₂ O , NiSO ₄ , NiSO ₄ .6H ₂ O, fatty acid nickel salt or nickel halide, etc., and one or a mixture of two or more thereof may be used.

In addition, as the manganese raw material, manganese oxides such as Mn ₂ O ₃ , MnO ₂ , and Mn ₃ O ₄ ; MnCO ₃ , Mn(NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylic acid salt, citric acid Examples include manganese salts such as manganese and fatty acid manganese salts; oxyhydroxides, manganese chloride, and the like, and any one or a mixture of two or more thereof may be used.

In addition, examples of the aluminum source material include AlSO ₄ , AlCl, and AlNO _3, and one or a mixture of two or more thereof may be used.

Next, an ammonium cation-containing complex-forming agent and a basic compound are added to the mixture of the metal raw material produced above, and coprecipitation reaction is carried out at pH 11 to pH 13 to obtain a metal-containing hydroxide or oxyhydroxide. A reaction solution in which seeds are produced can be manufactured.

The ammonium cation-containing complex-forming agent may be NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , or NH ₄ CO ₃ , or the like. Of course, one kind of these may be used alone, or a mixture of two or more kinds may be used. The ammonium cation-containing complex-forming agent may be used in the form of an aqueous solution, in which case the solvent is water or an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.). A mixture of water may be used.

The ammonium cation-containing complex forming agent may be added in an amount of 0.5 to 1 with respect to 1 mol of the mixture of the metal raw material. Generally, a chelating agent reacts with a metal at a molar ratio of 1:1 or more to form a complex, but an unreacted complex that has not reacted with a basic aqueous solution becomes an intermediate product among the formed complexes. Instead, since the chelating agent can be recovered and reused, the amount of the chelating agent used in the present invention can be reduced more than usual. As a result, the crystallinity of the positive electrode active material can be enhanced and stabilized.

The basic compound may be an alkali metal or alkaline earth metal hydroxide such as NaOH, KOH or Ca(OH) ₂ or a hydrate thereof, and one of these may be used alone or two or more of them may be used. Mixtures may be used. The basic compound may also be used in the form of an aqueous solution, in which case the solvent is water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.) and water. May be.

In addition, the coprecipitation reaction for forming the seed of the metal-containing hydroxide or oxyhydroxide may be performed under the condition that the pH is 11 to 13. If the pH deviates from the above range, it may change the size of the produced hydroxide or oxyhydroxide or induce particle cracking. Further, metal ions may be eluted on the surface of the hydroxide or oxyhydroxide, and various oxides may be formed by a side reaction. More specifically, it may be performed under the condition that the pH of the mixed solution is 11-12.

In order to satisfy the above pH range, the ammonium cation-containing complexing agent and the basic compound may be used in a molar ratio of 1:10 to 1:2. In this case, the pH value means a pH value at a liquid temperature of 25°C.

The coprecipitation reaction may be performed at a temperature of 40° C. to 70° C. under an inert atmosphere such as nitrogen. In addition, a stirring step may be selectively performed to increase the reaction rate during the reaction, and the stirring rate may be 100 rpm to 2000 rpm.

The metal-containing hydroxide or oxyhydroxide seeds are generated and deposited in the reaction solution by the steps described above. Specifically, the metal-containing hydroxide or oxyhydroxide may include a compound represented by Chemical Formula 2 below.

(Chemical formula 2)
Ni _1-x1-y1 Co _x1 M1 _y1 M3 _z1 M2 _w1 A

(In the chemical formula 2,
M1 is at least one selected from the group consisting of Al and Mn, and M2 is any one or more elements selected from the group consisting of Zr, Ti, Mg, Ta and Nb. And M3 is one or more elements selected from the group consisting of W, Mo and Cr, and 0<x1≦0.5, 0<y1≦0.5, 0.0005 ≦z1≦0.03, 0≦w1≦0.02, 0<x1+y1≦0.7, and A is a hydroxy group or an oxyhydroxy group. )

Further, the precipitated metal-containing hydroxide or oxyhydroxide may be selectively subjected to a drying step after separation according to a usual method.

The drying step may be performed according to a normal drying method, and specifically, may be performed for 15 to 30 hours by a method such as heat treatment in a temperature range of 100 to 200° C. or hot air injection.

Next, in the manufacturing method for manufacturing the positive electrode active material, step 2 is a step of growing the seed of the metal-containing hydroxide or oxyhydroxide manufactured in step 1 to manufacture particles.

Specifically, the ammonium cation-containing complex forming agent and the basic compound are added to the reaction solution in which the seed of the metal-containing hydroxide or oxyhydroxide is formed, and the pH of the reaction solution is higher than the pH during the coprecipitation reaction. Particles of the metal-containing hydroxide or oxyhydroxide can be grown by adding it until it becomes low.

The step of growing particles of the metal-containing hydroxide or oxyhydroxide comprises adding a mixture of the first metal source material including a nickel source material, a cobalt source material, and an M1-containing source material to the first metal source material. The mixture ratio of the second metal source material containing nickel, cobalt, and M1 containing source material in different concentrations from the mixture is gradually changed from 100% by volume to 0% by volume. So added.

Thus, by continuously increasing the amount of the mixture of the second metal source material to the mixture of the first metal source material and controlling the reaction rate and reaction time, nickel, cobalt and M1 are Independently, metal-containing hydroxides or oxyhydroxides can be produced that exhibit a continuously varying concentration gradient from the center of the particle to the surface. At this time, the concentration gradient and the gradient of the metal in the generated hydroxide or oxyhydroxide are the composition of the mixture of the first metal source material and the mixture of the second metal source material and the ratio of the mixed supply. In order to make a high density state in which the concentration of a specific metal is high, it is preferable to increase the reaction time and decrease the reaction rate, and a low density state in which the concentration of a specific metal is low. It is preferable to shorten the reaction time and increase the reaction rate in order to produce

Specifically, the rate of the mixture of the second metal source material added to the mixture of the first metal source material is continuously increased within the range of 1 to 30% with respect to the initial uptake rate. Can be done. Specifically, the uptake rate of the first metal source material mixture may be 150 ml/hr to 210 ml/hr, and the uptake rate of the second metal source material mixture may be 120 ml/hr to 180 ml. /Hr, and the uptake rate of the mixture of the second metal source materials may be continuously increased within the range of 1% to 30% with respect to the initial uptake rate within the uptake rate range. At this time, the reaction may be performed at 40°C to 70°C. In addition, the size of the precursor particles can be adjusted by adjusting the supply amount and the reaction time of the mixture of the second metal source material with respect to the mixture of the first metal source material.

The step of growing the metal-containing hydroxide or oxyhydroxide particles in step 2 may be performed at a lower pH than the step of forming the metal-containing hydroxide or oxyhydroxide particles in step 1. Specifically, it may be carried out at a pH lower than that in step 1 and higher than or equal to pH 8 and lower than pH 11, and more specifically in the range of pH 8 to 10.5.

The step of growing the metal-containing hydroxide or oxyhydroxide particles may be performed by changing the pH of the reaction product to a rate of pH 1 to 2.5 per hour. As described above, a desired particle structure can be easily formed by performing the reaction at a pH lower than that in the coprecipitation reaction at the above-described pH change rate.

Further, when incorporating the ammonium cation-containing complex-forming agent and the basic compound into the reaction solution in which the particles of the metal-containing hydroxide or oxyhydroxide are formed, they may be incorporated at the same rate, or the incorporation rate may be continuous. You may reduce and take in. When capturing at a reduced capture rate, the capture rate can be reduced at a rate reduction rate of 20% or more and less than 100%.

As described above, the deposition rate and concentration of the ammonium cation-containing complex forming agent and the basic compound, and the reaction temperature are controlled to control the deposition rate of the metal-containing hydroxide or oxyhydroxide in the particle growth step in Step 1. The deposition rate of the metal-containing hydroxide or oxyhydroxide can be faster than that of As a result, the density of the metal-containing hydroxide or oxyhydroxide particles serving as a precursor in the vicinity of the outer surface of the particles can be lowered to easily induce the particle growth direction during the subsequent heat treatment process.

In addition, the step 2 is preferably performed in an inert atmosphere.

After the step of step 2, a step of separating the grown metal-containing hydroxide or oxyhydroxide particles from the reaction solution, and then washing and drying may be selectively performed.

The drying step may be performed according to a usual drying method, and specifically, may be performed by a method such as heat treatment in a temperature range of 100° C. to 120° C. or hot air injection.

Next, in the manufacturing method for manufacturing the positive electrode active material, in step 3, the particles of the metal-containing hydroxide or oxyhydroxide grown in step 2 are used as a lithium source material and an M3 source material, optionally. A step of manufacturing a positive electrode active material having a structure in which a buffer layer is interposed between a core and a shell by mixing the M2 raw material with a heat treatment. At this time, the M2 raw material is as described above.

The heat treatment process may be performed at 250° C. to 1000° C., or 800° C. to 900° C. If the heat treatment temperature is less than 250° C., the reaction between the compounds used is not sufficient, and if it exceeds 1000° C., an unstable structure may be formed due to evaporation of Li in the crystal structure. ..

The heat treatment process may be performed in multiple steps of 2 to 3 by adding a low temperature heat treatment process in order to maintain the concentration gradient and the grain orientation. Specifically, it may be carried out by a method of maintaining at 250 to 450°C for 5 to 15 hours, at 450 to 600°C for 5 to 15 hours, and at 700 to 900°C for 5 to 15 hours.

Although the time for performing the heat treatment step varies depending on the heat treatment temperature, it is easy to control the particle shape by performing the heat treatment step under the above-mentioned temperature conditions for 5 hours to 48 hours, or for 10 hours to 20 hours. Specifically, during the heat treatment, if the temperature is less than 5 hours, crystallization may not be performed, and if it exceeds 48 hours, excessive crystallization may occur or Li in the crystal structure may be generated. Evaporation can form an unstable structure.

The metal-containing hydroxide or oxyhydroxide particles generated and grown in Steps 1 and 2 are formed inside the particles due to the process conditions during the manufacturing process, that is, due to a difference in pH and the like, and thereafter by particle growth. The crystals outside the particles have different properties. That is, the internal crystal formed when the pH is high contracts during the heat treatment process described above, and the crystal formed at the low pH and temperature grows. Therefore, the contracted crystal forms a core, and the crystal grown outside forms a shell, and the formation of the core and the shell forms a void between the core and the shell, and between the core and the shell. The crystals located form a three-dimensional network that connects the core and shell of the particles. Further, the crystal (shell) outside the particle grows radially from the center of the particle to have crystal orientation.

Examples of the lithium-containing raw material include lithium-containing carbonates (eg, lithium carbonate), hydrates (eg, lithium hydroxide monohydrate (LiOH.H ₂ O)), hydroxides (eg, water). Lithium oxide, etc., nitrates (eg, lithium nitrate (LiNO ₃ ), etc.), chlorides (eg, lithium chloride (LiCl) etc.) and the like, and one of these may be used alone or a mixture of two or more thereof may be used. Good. Further, the amount of the lithium-containing raw material used may be determined according to the content of lithium and the composite metal in the finally produced lithium mixed metal oxide, specifically, in the lithium raw material It may be used in an amount such that the molar ratio (molar ratio of lithium/metal element (Me)) to the contained lithium and the metal element (Me) contained in the metal-containing hydroxide is 1.0 or more. ..

As the M3 raw material, acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide containing M3 element may be used. As an example, when M3 is W, tungsten oxide may be used. The M3 raw material may be used in a range that satisfies the content condition of the M3 element in the finally manufactured positive electrode active material.

When the metal-containing hydroxide or oxyhydroxide is mixed with the lithium-containing raw material, a sintering agent may be selectively added. Wherein the sintering Yuizai, _{specifically, NH 4 F, NH 4 NO} 3, or _{(NH 4)} a compound containing ammonium ions, such as 2 SO _4; such as B 2 _{O 3} or _Bi 2 _{O 3} It may be a metal oxide; or a metal halide such as NiCl ₂ or CaCl ₂ , and any one or a mixture of two or more thereof may be used. The sintering agent may be used in an amount of 0.01 to 0.2 mol based on 1 mol of the positive electrode active material precursor. If the content of the sintering agent is too low, less than 0.01 mol, the effect of improving the sintering characteristics of the positive electrode active material precursor is not so great, and the content of the sintering agent exceeds 0.2 mol. If it is too high, the performance as the positive electrode active material may be deteriorated by the excessive amount of the sintering agent, and the initial capacity of the battery may be decreased during the progress of charging and discharging.

A sintering aid may be selectively added during the heat treatment process.

Crystals can be easily grown at low temperature when a sintering aid is added, and heterogeneous reactions can be minimized during dry mixing. Further, the sintering aid has the effect of blunting the corner portions of the lithium composite metal oxide primary particles to form round curved particles. Generally, in a lithium oxide-based positive electrode active material containing manganese, manganese is frequently eluted from the corners of the particles, and the elution of manganese reduces the characteristics of the secondary battery, particularly the life characteristics at high temperatures. On the other hand, when a sintering aid is used, by rounding the corners of the primary particles, the elution site of manganese can be reduced, and as a result, the stability and life characteristics of the secondary battery can be improved. You can

Specifically, the sintering aid is a boron compound such as boric acid, lithium tetraborate, boric oxide and ammonium borate; cobalt (II) oxide, cobalt (III) oxide, cobalt (IV) oxide and tetraborate. Cobalt compounds such as tricobalt oxide; vanadium compounds such as vanadium oxide; lanthanum compounds such as lanthanum oxide; zirconium compounds such as zirconium boride, calcium zirconium silicate and zirconium oxide; yttrium compounds such as yttrium oxide; or gallium oxide, etc. Examples thereof include gallium compounds, and any one of these compounds or a mixture of two or more thereof may be used.

The sintering aid may be used in an amount of 0.2 to 2 parts by weight, more specifically 0.4 to 1.4 parts by weight, based on the total weight of the precursor. ..

Further, when the metal-containing hydroxide or oxyhydroxide and the lithium-containing raw material are mixed, a moisture removing agent may be selectively further added. Specifically, examples of the water removing agent include citric acid, stannic acid, glycolic acid, and maleic acid, and any one or a mixture of two or more thereof may be used. The water removing agent may be used in an amount of 0.01 to 0.2 mol based on 1 mol of the positive electrode active material precursor.

In addition, the heat treatment process for the mixture containing the metal-containing hydroxide or oxyhydroxide particles and the lithium source material, the M3 source material, and optionally the M2 source material may be performed in an air atmosphere or an oxidizing atmosphere (for example, O ₂ or the like). ) Is possible, and more specifically, it may be performed in an oxidizing atmosphere.

Meanwhile, a water washing process for removing impurities existing on the surface may be selectively further performed on the positive electrode active material manufactured after the heat treatment process.

The water washing step may be performed by a usual method, and specifically, may be performed by washing with water or a lower alcohol having 1 to 4 carbon atoms.

The method for manufacturing a positive electrode active material according to an embodiment of the present invention may further include a step of forming a surface treatment layer on the surface of the positive electrode active material after the manufacturing process of the positive electrode active material containing the lithium mixed metal oxide. Good.

The step of forming the surface treatment layer may be performed according to a usual method for forming the surface treatment layer, such as a solid phase synthesis method or a wet method, except that the raw material containing the coating element for forming the surface treatment layer is used. The coating element is as described above.

Specifically, when the solid phase synthesis method is used, a surface treatment layer containing a coating element-containing compound is formed on the surface of the positive electrode active material by dry-mixing the produced positive electrode active material and the boron-containing compound and then heat-treating them. Can be formed. When the surface treatment layer is formed by the solid phase synthesis method as described above, a uniform surface treatment layer can be formed without fear of damage to the positive electrode active material.

As an example, when the coating element is boron (B), the boron-containing compound may be, specifically, a boron-containing oxide, a hydroxide, an alkoxide or an acryl compound. More _{specifically, H 3 BO 3, B 2} O 3, C 6 H 5 B (OH) 2, (C 6 H 5 O) 3 B, [CH 3 (CH 2) 30] 3 B, C 3 For example, H ₉ B ₃ O ₆ or (C ₃ H ₇ O) ₃ B may be used, and any one or a mixture of two or more thereof may be used.

The amount of the boron-containing compound used may be an appropriate amount in consideration of the content of boron or the content of boron lithium oxide in the finally manufactured surface treatment layer. Specifically, the boron-containing compound is used in an amount of 0.05 to 1 part by weight, more specifically 0.1 to 0.8 part by weight, based on 100 parts by weight of the positive electrode active material. May be.

The dry mixing method is a mortar grinder mixing method using mortar; or a roll mill, a ball mill, a high energy ball mill, and a planetary mill. A uniform surface treatment may be performed using a mixing method using a mechanical milling method such as a planetary mill, a stirred ball mill, a vibrating mill, or a jet-mill. Considering the formation of layers, the dry mixing method may more specifically be performed using a mechanical milling method.

The heat treatment may be performed near the melting point of the boron-containing compound. For example, the melting point of the boron-containing compound may be 130°C to 500°C. When the heat treatment of the boron-containing compound is carried out in the above-mentioned temperature range, the boron-containing compound is melted and flows by the heat treatment, reacting with at least a part of lithium impurities present on the lithium mixed metal oxide, and boron. The containing compound can be easily converted to boron lithium oxide and coated on the surface of the lithium metal oxide. As described above, the conversion of the lithium impurities into boron lithium oxide can reduce the amount of lithium impurities existing on the lithium mixed metal oxide. It is also possible to form a surface-treated layer in which boron lithium oxide is uniformly applied to the surface of the lithium mixed metal oxide in an amount proportional to the amount of the boron-containing compound used even at a low heat treatment temperature.

More specifically, the heat treatment of the boron-containing compound may be performed at 130° C. to 500° C., more specifically at 130° C. to 500° C., for 3 hours to 10 hours. When the heat treatment temperature is lower than 130° C., the boron-containing compound is not sufficiently melted and the boron-containing compound remains as it is on the lithium mixed metal oxide, or even if it is converted to boron lithium oxide, a uniform surface treatment is performed. If the layer cannot be formed and the temperature is higher than 500° C., the reaction is excessively rapid due to the high temperature, and a uniform surface treatment layer cannot be formed on the surface of the lithium mixed metal oxide.

When the surface treatment layer contains aluminum, the surface treatment layer can be formed on the surface of the positive electrode active material by mixing the manufactured positive electrode active material with the aluminum-containing raw material and then performing heat treatment. At this time, the aluminum-containing raw material may be Al ₂ O _3, etc., which enables uniform coating at the time of forming the surface treatment layer, can form single particles even at a low temperature, and It may have an average particle size of 100 nm or less, more specifically 50 to 80 nm, so that the change in the crystal structure of the formed metal oxide can be suppressed after the formation of the treatment layer.

The heat treatment of the aluminum-containing compound may be performed at 300°C to 500°C. When the heat treatment temperature is lower than 300° C., even a coated oxide having a thickness of 100 nm or less does not crystallize, so that when this active material is applied to a battery, migration of lithium ions can be hindered. Further, if the heat treatment temperature is higher, the evaporation of lithium occurs, the crystallinity of the metal oxide layer formed on the surface increases, and a problem occurs in the movement of Li ⁺ . In addition, when the heat treatment time is excessively long, evaporation of lithium occurs, the crystallinity of the metal oxide layer formed on the surface becomes high, and a problem may occur in the movement of Li ⁺ .

On the other hand, in the case of using the wet method, the coating material containing a coating element for forming a surface treatment layer is dissolved or dispersed in a solvent to produce a composition for forming a surface treatment layer, which is then subjected to an ordinary slurry coating method, specifically The surface-treated layer may be formed by treating the surface of the positive electrode active material using a method such as coating, spraying or dipping and then drying.

At this time, the coating element-containing raw material is as defined above, the solvent may be appropriately selected depending on the type of the raw material, and the raw material can be dissolved or uniformly dispersed. Any material can be used without particular limitation.

The surface treatment layer forming step may be performed once, or may be performed twice or more so that a surface treatment layer having a multilayer structure of two or more layers can be formed on the surface of the positive electrode active material. Specifically, after the primary surface treatment with the boron-containing raw material for the positive electrode active material, the secondary surface treatment step with the aluminum-containing raw material for the resulting first surface treatment layer forming positive electrode material. May be performed.

The positive electrode active material produced by the above-described production method controls the pH, concentration, and rate of the reaction product, and includes a buffer layer including voids provided between the core and the shell, so that the positive electrode active material can be used in the electrode production process. The destruction of the active material during rolling is minimized, the reactivity with the electrolyte is maximized, and the particles forming the shell have a crystal structure with an orientation that facilitates insertion and desorption of lithium ions. It is possible to reduce the resistance of the battery and improve the life characteristics. Further, in the positive electrode active material, the specific surface area, the average particle diameter, and the specific surface area are both controlled, so that the battery capacity characteristics can be further improved, and further, the distribution of the transition metal is controlled over the entire active material particles. If so, it exhibits high capacity, long life and thermal stability when applied to a battery, and can minimize performance deterioration at high voltage.

Therefore, according to still another embodiment of the present invention, there is provided a positive electrode and a lithium secondary battery including the positive electrode active material described above.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material described above.

The positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and is, for example, stainless steel, aluminum, nickel, titanium, calcined carbon or aluminum or stainless steel. Those whose surface is subjected to surface treatment with carbon, nickel, titanium, silver or the like may be used. In addition, the positive electrode current collector may have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. .. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foamed body, and a non-woven body.

In addition, the positive electrode active material layer may include a conductive material and a binder in addition to the above positive electrode active material.

At this time, the conductive material is used to give conductivity to the electrodes, and can be used without particular limitation as long as it does not cause a chemical change and has electronic conductivity in the constructed battery. Is. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber; copper, nickel, aluminum, Examples include metal powders or metal fibers such as silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and one of these alone. Alternatively, a mixture of two or more kinds may be used. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

In addition, the binder plays a role of improving adhesion between particles of the positive electrode active material and adhesion between the positive electrode active material and the current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, Regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like, One of these may be used alone, or a mixture of two or more may be used. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a general method for manufacturing a positive electrode, except that the above-mentioned positive electrode active material is used. Specifically, the positive electrode active material described above, and, optionally, a positive electrode active material layer-forming composition containing a binder and a conductive material is applied on a positive electrode current collector, and then produced by drying and rolling. Good. At this time, the types and contents of the positive electrode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone). Alternatively, water or the like may be used, and one type of these may be used alone or a mixture of two or more types may be used. The amount of the solvent used is, in consideration of the coating thickness of the slurry and the manufacturing yield, dissolving or dispersing the positive electrode active material, the conductive material and the binder, and thereafter, at the time of coating for manufacturing the positive electrode, an excellent thickness. It suffices that the viscosity has a homogeneity.

Further, as another method, the positive electrode is formed by casting the composition for forming a positive electrode active material layer on another support, and then peeling the film from the support to laminate a film obtained on the positive electrode current collector. It may be manufactured by

According to another embodiment of the present invention, there is provided an electrochemical device including the positive electrode. The electrochemical device may be, for example, a battery or a capacitor, or more specifically, a lithium secondary battery.

Specifically, the lithium secondary battery includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is the above-mentioned. It is as follows. Further, the lithium secondary battery may optionally further include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode, and a separator, and a seal member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, and firing. Carbon, copper or stainless steel whose surface is subjected to surface treatment with carbon, nickel, titanium, silver or the like, or aluminum-cadmium alloy may be used. In addition, the negative electrode current collector may have a thickness of 3 to 500 μm, and like the positive electrode current collector, fine unevenness is formed on the surface of the current collector to bond the negative electrode active material. You can also strengthen your power. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam and a non-woven fabric.

The negative electrode active material layer selectively contains a binder and a conductive material together with the negative electrode active material. The negative electrode active material layer, as an example, a negative electrode active material on the negative electrode current collector, and selectively apply a negative electrode forming composition containing a binder and a conductive material and dried, or the negative electrode forming composition. It may be manufactured by casting on another support and then peeling the film obtained from this support and laminating the resulting film on the negative electrode current collector.

A compound capable of reversibly intercalating and deintercalating lithium may be used as the negative electrode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn. Metallic compounds capable of alloying with lithium, such as alloys or Al alloys; Doping and dedoping with lithium such as SiO _x (0<x<2), SnO ₂ , vanadium oxide, lithium vanadium oxide A metal oxide capable of forming a metal oxide; or a composite including the above-mentioned metallic compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite family. Mixtures may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. Further, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. The low crystalline carbon is typified by soft carbon and hard carbon, and the high crystalline carbon is amorphous, platy, scaly, spherical or fibrous natural graphite or Artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, mesocarbon microbeadsph and coal, and mesophase. Typical examples are high-temperature calcined carbon such as petroleum or coal tar pitch delivered cokes.

Moreover, the binder and the conductive material are as described for the positive electrode.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, the separator is not particularly limited as long as it is used as a separator in a lithium secondary battery. It can be used without any use, and it is particularly preferable that it has a low resistance to the movement of ions of the electrolyte and is excellent in the wettability of the electrolytic solution. Specifically, a porous polymer film, for example, a porous polymer film produced from a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, or A laminated structure having two or more layers of these may be used. Further, a usual porous non-woven fabric, for example, a non-woven fabric composed of high melting point glass fiber, polyethylene terephthalate fiber or the like may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and optionally, a single layer or a multi-layer structure may be used. Good.

Further, as the electrolyte used in the present invention, an organic liquid electrolyte that can be used during the production of a lithium secondary battery, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic Examples thereof include electrolytes and the like, but are not limited thereto.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent can be used without particular limitation as long as it plays a role of a medium that allows ions involved in the electrochemical reaction of the battery to move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; dibutyl ether. Ether solvents such as (dibutyl ether) or tetrahydrofuran (tetrahydrofuran); ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (dimethylcarbonate). ), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (polyethylene carbonate, etc.), propylene carbonate, etc. An alcohol solvent such as ethanol or isopropyl alcohol; R—CN (R is a C2-C20 linear, branched or cyclic hydrocarbon group, and may contain a double bond aromatic ring or an ether bond; ) And the like; amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes and the like may be used. Among these, carbonate solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) capable of enhancing the charge/discharge performance of the battery, and chain carbonate compounds having a bottom viscosity More preferred is a mixture of (eg ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate etc.). In this case, when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9, the electrolytic solution can exhibit excellent performance.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium _{salt, LiPF 6, LiClO 4, LiAsF} 6, LiBF 4, LiSbF 6, LiAlO 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO _{3) 2, LiN (C 2} F 5 SO 2) 2, LiN (CF 3 SO 2) 2 · LiCl, LiI , or _{LiB (C 2} O _4), etc. ₂ may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can effectively move.

In addition to the electrolyte constituents, the electrolyte includes, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate for the purpose of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Compound, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme (glyme), hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, One or more additives such as ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum (III) chloride may be further included. At this time, the additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

As described above, the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, and is therefore suitable for portable use in mobile phones, notebook computers, digital cameras, etc. It is useful in the field of electric vehicles such as equipment and hybrid electric vehicles (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or Any one or more of the power storage systems may be used as a power source for medium and large-sized devices.

<Example>
Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily carry out the invention. However, the invention may be embodied in various different forms and is not limited to the embodiments described herein.

[Example 1: Production of positive electrode active material]
In a batch type 5 L reactor set at 60° C., nickel sulfate, cobalt sulfate and manganese sulfate were mixed in water at a molar ratio of 80:10:10 to prepare a 2M first mixture. A mixed solution of metal source materials was prepared. Separately from this, nickel sulfate, cobalt sulfate and manganese sulfate were mixed in water at a molar ratio of 40:30:30 to prepare a mixed solution of a 2M second metal source material. The container filled with the mixed solution of the first metal source material is connected so as to enter the reactor, and the container filled with the mixed solution of the second metal source material is the mixture of the first metal source material. It was connected to enter a container filled with the solution. Furthermore, a 4M NaOH solution and a 7% NH ₄ OH aqueous solution were prepared, and each was connected to a reactor.

After putting 3 liters of deionized water into the coprecipitation reactor (capacity: 5 L), nitrogen gas was purged into the reactor at a rate of 2 liters/minute to remove dissolved oxygen in the water, and The atmosphere was oxidizing. Then, after taking up 100 ml of 4 M NaOH, the pH was maintained at 12.0 at a stirring speed of 1200 rpm at a temperature of 60°C.

Next, the mixed solution of the first metal source material was taken in at a rate of 180 ml/hr, the NaOH aqueous solution at 180 ml/hr, and the NH ₄ OH aqueous solution at a rate of 10 ml/hr, respectively, and reacted at pH 12 for 30 minutes to react the first metal. A hydroxide seed of a mixed solution of raw materials was formed. Next, the amounts of NaOH and NH ₄ OH are gradually reduced to lower the pH at a rate of pH 2 per hour, the pH is changed to 10, and the mixed solution of the second metal raw material is mixed with the first metal raw material. The mixed solution was introduced into a container at 150 ml/hr to induce the growth of hydroxide particles and induce a concentration gradient inside the particles. Next, the reaction was maintained for 36 hours to grow metal-containing hydroxide particles. The resulting metal-containing hydroxide particles were separated, washed with water and dried in an oven at 120°C.

Using the metal-containing hydroxide particles prepared above as a lithium source material, lithium hydroxide and tungsten oxide were mixed at a molar ratio of 1:1.07:0.2, and then at 300° C. for 10 hours at 500° C. Heat treatment was performed for 10 hours at 820° C. for 10 hours. As a result, the internal crystal produced when the pH is high contracts, the crystal produced when the pH is low grows to form a core and a shell, and a void is formed between the core and the shell and the core and the shell. The crystal located between the shell and the shell formed a three-dimensional network structure to produce a positive electrode active material including a core, a shell, and a buffer layer structure.

[Example 2: Production of positive electrode active material]
1% by weight of alumina (Al ₂ O ₃ ) particles having a size of 100 nm was mixed with the positive electrode active material manufactured in Example 1 and heat-treated at a temperature of 400° C. for 5 hours in the atmosphere to form a surface treatment layer.

[Example 3: Production of positive electrode active material]
Boric acid (manufactured by Samchun Pure Chemicals Co., Ltd.) was mixed in an amount of 0.1% by weight with respect to the positive electrode active material manufactured in Example 1 and heat-treated in the air at a temperature of 400° C. for 5 hours to form a surface-treated layer.

[Comparative Example 1: Production of positive electrode active material]
In a batch type 5L reactor set at 60° C., nickel sulfate, cobalt sulfate and manganese sulfate were mixed in water at a molar ratio of 60:20:20, and a metal salt solution having a concentration of 2M was prepared. Prepared. The container filled with the metal salt was connected so as to enter the reactor, a 4M NaOH solution and a 7% NH ₄ OH aqueous solution were prepared, and each container was connected to the reactor.

After putting 3 liters of deionized water into the coprecipitation reactor (volume: 5 L), nitrogen gas was purged into the reactor at a rate of 2 liters/minute to remove dissolved oxygen in the water, and The atmosphere was oxidizing. Then, after taking up 100 ml of 4 M NaOH, the pH was maintained at 12.0 at a stirring speed of 1200 rpm at a temperature of 60°C.

Next, the metal salt solution was taken in at a rate of 180 ml/hr, the NaOH aqueous solution was taken in at a rate of 180 ml/hr, and the NH ₄ OH aqueous solution was taken in at a rate of 10 ml/hr, and reacted for 36 hours to form nickel manganese cobalt-based composite metal hydroxide particles. did.

The resulting nickel-manganese-cobalt-based composite metal hydroxide particles were mixed with lithium hydroxide as a lithium source material at a molar ratio of 1:1.07, and then mixed under an oxygen atmosphere (oxygen partial pressure 20%). Then, heat treatment was performed at 820° C. for 10 hours to manufacture a positive electrode active material.

[Production Example: Production of lithium secondary battery]
A lithium secondary battery was manufactured using each of the positive electrode active materials manufactured in Example 1 and Comparative Example 1.

Specifically, the positive electrode active material prepared in Example 1 and Comparative Example 1, the carbon black conductive material, and the PVdF binder were mixed in a N-methylpyrrolidone solvent at a weight ratio of 95:2.5:2.5. Then, a positive electrode-forming composition (viscosity: 5000 mPa·s) was produced, applied to an aluminum current collector, dried at 130° C., and rolled to produce a positive electrode.

Further, as a negative electrode active material, natural graphite, a carbon black conductive material and a PVdF binder are mixed in a N-methylpyrrolidone solvent at a weight ratio of 85:10:5 to prepare a negative electrode forming composition. The negative electrode was manufactured by coating on a current collector.

An electrode assembly is manufactured by interposing a porous polyethylene separator between the positive electrode and the negative electrode manufactured as described above, and the electrode assembly is placed inside the case. A lithium secondary battery was manufactured by injection. At this time, the electrolytic solution is a lithium hexafluorophosphate (LiPF 6) having a concentration of 1.0 M in an organic solvent composed of ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (mixing volume ratio of EC/DMC/EMC=3/4/3). ₆ ) was dissolved and manufactured.

[Experimental Example 1: Observation of structure of positive electrode active material]
The precursor prepared in Example 1 was observed with a field emission scanning electron microscope (FE-SEM), and the diameter and volume of the core and shell and the ratio in the active material were observed from the results. Calculated respectively. The results are shown in Table 1 below.

The cathode active material prepared in Example 1 was processed by ion milling, and then the cross-sectional structure of the cathode active material was observed using FE-SEM. The results are shown in Fig. 2.

As a result of confirming the cross-sectional structure, formation of a buffer layer containing a three-dimensional network structure in the core and shell was confirmed, and the particles in the shell showed crystal orientation from the center of the particle toward the surface. Is recognized. The total particle size of the positive electrode active material is 9.9 μm, the radius of the positive electrode active material is 4.95 μm, the thickness (radius) of the core portion 1 is 1.4 μm, and the thickness of the buffer layer is 1 μm. The thickness of the shell 2 was 0.7 μm, and the thickness of the shell 2 was 1.85 μm. When the porosity was calculated by converting the volume ratio from this, the porosity in the positive electrode active material was about 22% by volume.

[Experimental Example 2: Analysis of concentration gradient in positive electrode active material]
In addition, component analysis was performed on the positive electrode active material in Example 1 using EPMA. The results are shown in Table 2 below. In the table below, the Scan positions were set up from scan 1 to scan 5 according to the order as shown in FIG.

As shown in Table 2, it is recognized that the concentration of Ni is decreased from the center of the positive electrode active material toward the surface, and the concentrations of cobalt and manganese are included in an increasing concentration gradient.

[Experimental Example 3: Analysis of positive electrode active material]
The average particle size, the specific surface area and the rolling density of the positive electrode active materials produced in Examples 1 to 3 and Comparative Example 1 were measured, and the results are shown in Table 3 below.

(1) Average particle size (D ₅₀ ): introduced into a laser diffraction particle size measuring device (for example, Microtrac MT 3000) and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then 50% standard of particle size distribution in the measuring device. The average particle diameter (D ₅₀ ) can be calculated.

(2) BET specific surface area: The specific surface area of the positive electrode active material is measured according to the BET method, and specifically, using BELSORP-mino II manufactured by BEL Japan under liquid nitrogen temperature (77K). It can be calculated from the nitrogen gas adsorption amount of.

(3) Tap density: The tap density was measured using a tap density tester.

(4) Ni disorder degree (Ni disorder) and average particle size (crystal size) of crystal grains: Measured using an X-ray diffraction (XRD) analyzer.

The positive electrode active materials of Examples 1 to 3 according to the present invention had the same level of average particle size as Comparative Example 1 due to their unique structure, and showed increased BET specific surface area and porosity. .. However, in the case of the positive electrode active material of Example 3 in which the boron-containing surface treatment layer was formed, the BET specific surface area value was decreased by the boron component uniformly forming the protective film on the surface of the active material and relaxing the surface bending. Numerically, the result was slightly reduced as compared with Examples 1 and 2. Further, the positive electrode active materials of Examples 1 to 3 according to the present invention also showed lower Ni disorder and crystal grain size than Comparative Example 1 in terms of crystal grains.

[Experimental Example 4: Evaluation of positive electrode active material]
A coin cell (using a negative electrode of Li metal) manufactured by using the positive electrode active material manufactured in Examples 1 to 3 and Comparative Example 1 was charged at 25° C. until a constant current (CC) of 4.25 V of 0.1 C was obtained. Then, the battery was charged at a constant voltage (CV) of 4.25V, and the first charging was performed until the charging current reached 0.05 mAh. Next, after leaving it for 20 minutes, it was discharged at a constant current of 0.1 C until it reached 3.0 V, and the discharge capacity at the first cycle was measured. Next, the charging/discharging capacity, charging/discharging efficiency, and rate characteristics were evaluated under different discharge conditions from 2C. The results are shown in Table 4 below.

As a result of the experiment, the lithium secondary batteries containing the positive electrode active materials of Examples 1 to 3 were compared with the lithium secondary batteries containing the positive electrode active material of Comparative Example 1 in terms of charge/discharge efficiency, rate characteristics and capacity characteristics. All showed improved effects.

[Experimental Example 5: Evaluation of battery characteristics of lithium secondary battery]
The battery characteristics of the lithium secondary batteries containing the positive electrode active materials of Examples 1 to 3 and Comparative Example 1 were evaluated by the following methods.

Specifically, the lithium secondary battery was charged/discharged 800 times at a temperature of 25° C. within a driving voltage range of 2.8 V to 4.15 V under a condition of 1 C/2 C.

In order to evaluate the output characteristics, a battery charged and discharged at room temperature (25°C) was charged with SOC 50% as a reference and the resistance was measured. At low temperature (-30°C), a current was applied with SOC 50% as a reference. The width of the voltage drop was measured.

As a result, resistance at room temperature (25° C.) and low temperature (−30° C.), and cycle capacity retention rate (capacity), which is the ratio of the discharge capacity at the 800th cycle to the initial capacity after 800 charging/discharging operations at room temperature. Retention) was measured and is shown in Table 5 below.

As a result of the experiment, it was confirmed that the lithium secondary batteries using the positive electrode active materials manufactured in Examples 1 to 3 were superior to Comparative Example 1 in output characteristics at room temperature and low temperature, and cycle characteristics. Was given.

Claims (17)

With the core,
A shell located around the core,
A buffer layer that is located between the core and the shell and that connects the core and the shell and that includes a three-dimensional network structure and a void.
The three-dimensional network structure including the core, the shell, and the buffer layer independently includes a lithium mixed metal oxide represented by the following Chemical Formula 1 ,
The core is a secondary particle in which primary particles are aggregated,
BET specific surface area of 0.2m ² /g~0.5m ² / g, porosity is 30 vol%, an average particle diameter _{(D 50)} Ri 8μm~15μm der,
(Chemical formula 1)
Li _a Ni _1-x-y Co _x M1 _y M3 _z M2 _w O ₂
In Chemical Formula 1, M1 is at least one selected from the group consisting of Al and Mn, and M2 is any one selected from the group consisting of Zr, Ti, Mg, Ta, and Nb, or Two or more elements, M3 is any one or two or more elements selected from the group consisting of W, Mo and Cr, 1.0≦a≦1.5, 0<x≦ A positive electrode active material for a secondary battery , wherein 0.5, 0<y≦0.5, 0.0005≦z≦0.03, 0≦w≦0.02, and 0<x+y≦0.7 . Said nickel, M1 and at least one of metal elements of cobalt, the core, shows a concentration gradient continuously changing at any one area of the whole shell, and the active material particles, according to claim 1 two Positive active material for secondary battery. The positive electrode active material for a secondary battery according to claim 1 , wherein the content of nickel contained in the core is higher than the content of nickel contained in the shell. The positive electrode active material for a secondary battery according to claim 1 , wherein the content of cobalt contained in the core is smaller than the content of cobalt contained in the shell. The positive electrode active material for a secondary battery according to claim 1 , wherein the content of M1 contained in the core is smaller than the content of M1 contained in the shell. The nickel, cobalt and M1 each independently show a continuously changing concentration gradient over the entire active material particle,
The concentration of nickel decreases with a continuous concentration gradient from the center of the active material particles toward the surface,
The positive electrode active material for a secondary battery according to claim 1 , wherein the cobalt and M1 concentrations independently increase with a continuous concentration gradient from the center of the active material particles toward the surface. The positive electrode active material for a secondary battery according to claim 1 , wherein the M1 is manganese (Mn). The positive electrode active material is in the form of secondary crystal particles in which two or more primary crystal particles are aggregated, and includes a polycrystalline lithium composite metal oxide having an average size of the primary crystal particles of 60 nm to 200 nm. The positive electrode active material for a secondary battery according to claim 1. The positive electrode active material for a secondary battery according to claim 1, wherein the shell includes particles of a crystallographically oriented lithium mixed metal oxide radially grown from a center of the positive electrode active material toward a surface thereof. The positive electrode active material for a secondary battery according to claim 1, wherein the shell has a shell region determined according to the following mathematical formula 1 of 0.2 to less than 1.
(Formula 1)
Shell region=(radius of positive electrode active material−radius of core−thickness of buffer layer)/radius of positive electrode active material The ratio of the radius of the core to the radius of the positive electrode active material is more than 0 and less than 0.4, and the ratio of the length from the center of the positive electrode active material particles to the interface between the buffer layer and the shell with respect to the radius of the positive electrode active material particles. Is more than 0 and less than 0.7, the positive electrode active material for a secondary battery according to claim 1. Boron (B), aluminum (Al), titanium (Ti), silicon (Si), tin (Sn), magnesium (Mg), iron (Fe), bismuth (Bi), on the surface of the positive electrode active material particles. The positive electrode for a secondary battery according to claim 1, further comprising at least one surface treatment layer containing one or more coating elements selected from the group consisting of antimony (Sb) and zirconium (Zr). Active material. A mixture of a metal source material containing a nickel source material, a cobalt source material, and an M1 source material (where M1 is at least one element selected from the group consisting of Al and Mn), and an ammonium cation-containing complex. A step of mixing a forming agent and a basic compound and coprecipitating the mixture at pH 11 to pH 13 to prepare a reaction solution in which a seed of a metal-containing hydroxide or oxyhydroxide is produced;
A step of adding an ammonium cation-containing complex-forming agent and a basic compound to the reaction solution until the pH of the reaction solution becomes 8 or more and less than 11 to grow particles of the metal-containing hydroxide or oxyhydroxide;
The grown metal-containing hydroxide or oxyhydroxide particles are used as a lithium source material and an M3 source material (wherein M3 is one or more selected from the group consisting of W, Mo and Cr). after mixing of the elements in it), and look at including a step of heat treatment,
The nickel source material is Ni(OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni(OH) ₂ .4H ₂ O, NiC ₂ O ₂ .2H ₂ O, Ni(NO ₃ ) ₂ .6H ₂ O, NiSO. _{4, NiSO 4 · 6H 2 O} , fatty nickel salt, and is one or a mixture of two or more of nickel halides,
Said cobalt source _{material, Co (OH) 2, CoOOH} , Co (OCOCH 3) 2 · 4H 2 O, Co (NO 3) 2 · 6H 2 O, and Co _{(SO 4)} of the 2 · 7H ₂ O One or a mixture of two or more,
The M1 raw material is Mn ₂ O ₃ , MnO ₂ , Mn ₃ O ₄ , MnCO ₃ , Mn(NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, manganese citrate, fatty acid manganese chloride, manganese chloride. , AlSO ₄ , AlCl, and AlNO ₃ or a mixture of two or more thereof,
The ammonium cation-containing complexing agent may be one or more of NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , and NH ₄ CO ₃ . The method for producing a positive electrode active material for a secondary battery according to claim 1 , which is a mixture . Growing the metal-containing hydroxide or oxyhydroxide particles comprises:
Nickel raw material, a mixture of the first metal source material containing cobalt raw material and M 1 raw material substance, nickel at different concentrations with a mixture of the first metal source material, cobalt, M 1 raw material substance The secondary method according to claim 13 , further comprising the step of adding a mixture of the second metal source material containing therein such that the mixing ratio gradually changes from 100% by volume to 0% by volume to 0% by volume: 100% by volume. A method for producing a positive electrode active material for a battery. Boron (B), aluminum (Al), titanium (Ti), silicon (Si), tin (Sn), magnesium (Mg), iron (Fe) are added to the positive electrode active material manufactured as a result of the heat treatment process. ), bismuth (Bi), further comprising forming a surface treatment layer containing either one or more coating element selected from the group consisting of antimony (Sb) and zirconium (Zr), claim 13 The method for producing a positive electrode active material for a secondary battery according to. Positive electrode active material containing a positive electrode for a secondary battery according to any one of claims 1 to 12. A lithium secondary battery comprising the positive electrode according to claim 16 .

Images